The invention generally relates to air bags and more particularly to air bags having a novel seam construction. While the present invention is applicable to many types of air bags, it will find favor with air bags that are designed to stay inflated for extended periods of time. For example, an air bag used to provide occupant protection during a rollover accident is one type of bag designed to stay inflated for a relatively long period. Generally, a rollover type of air bag would also include most if not all side impact air bags including seat mounted, vehicle frame-mounted or door-mounted, or side curtain air bags.
Historically, air bags have been made by sewing facing or adjacent panels of material together along a seam. The seam may include one or more rows of thread. To keep gas pressure in an air bag for longer durations, the panels can be made from low permeability woven fabric or made using woven fabric that is appropriately coated, typically by silicone or urethane. Depending on its application, the coating layer can be on the inside or the outside of the air bag. A portion of the prior art seam 21 is diagrammatically shown in FIG. 1. However, in the context of a long duration air bag, this type of seam has its deficiencies.
Any seam, including seam 21, must be sufficiently robust and stay together while the air bag is inflated. A sewn seam has proven to be both a cost-effective way of joining mating panels together and one that provides the required strength. However, the process of sewing creates many hundreds of needle/thread holes in the panels. Even though each needle/thread hole is very small, they collectively present a relatively large flow area through which inflation gas can escape from the air bag and in between fabric panels. FIG. 1 diagrammatically illustrates inflation gas escaping through the needle/thread holes. Additionally, as the air bag panels are pulled apart at the seam during inflation, the size of these needle/thread holes will increase, increasing the amount of pressure lose.
The prior art shows techniques that try to avoid the problems related to needle/thread holes. For example, the prior art has recognized that the needle/thread holes can be sealed after the panels are sewn together. However, this post-sewing, sealing step is undesirable because the sealing material is typically sticky (at least just after it is applied) and creates many manufacturing and handling related problems. Furthermore, it does not effectively seal the stretching of needle holes due to pressure. These deficiencies in the prior art are obviated by the present invention.
Further, the prior art shows using knitted or woven bags, which eliminate or at least minimize the number and length of sewn seams in the bag. This type of construction, however, requires a significant financial investment in complicated weaving or knitting equipment and still requires the air bag to be coated after it is formed and often does not totally eliminate the need for some type of sewn seam. The prior art has also suggested using microwave or radio frequency energy to weld polyurethane or urethane-coated material and/or panels together. As can be appreciated, these processes also require special equipment and elaborate manufacturing steps, outside of conventional air bag manufacturing processes, each of which significantly add to the cost of and the time to produce an air bag. The welded seam or seal by itself is not strong in tension (a pealing load) and as such this type of seam (or seal) can be more easily pulled apart than can a sewn seam.
It is an object of the present invention to provide a long-duration-pressure-sustaining air bag.
A further object of the present invention is to provide such an air bag that is constructed with machinery no more complicated than a sewing machine or at most a sewing machine in combination with RF welding equipment. The RF weld will provide a sealing mechanism only, not a structural seam.
It is a further object of the invention to form a pressure barrier upstream of a sewn seam, the pressure barrier shielding the structural sewn seam from the pressurized inflation gas within the air bag.
Accordingly the invention comprises: a safety apparatus including an air bag. The apparatus may also include an inflator, housing and/or manifold. The air bag comprises a first and second panel of flexible, material of relatively low permeability, wherein each panel has a respective, mating peripheral edge. In the preferred embodiment the panels are about the same size, but this is not a requirement of the invention. The first and second panels are joined together at least generally along or parallel to the peripheral edges of the panels to define an inflatable chamber therebetween. The structural seam or joint may extend about the entire air bag or only about a portion of the periphery of the air bag. The structural first seam is subject to a peel load or thread tension load as the first and second panels are urged or pulled apart as the air bag is inflated. The air bag also includes inlet means to receive an inflator or at least some source of inflation gas. The inlet means may also include a passage through which inflation gas is communicated into the air bag from a remotely positioned inflator. The air bag also includes a pressure barrier. The pressure barrier is located on the inside of the air bag upstream of the sewn, structural first seam or joint. The pressure barrier comprises a thin and narrow strip of material that is preferably sewn or bonded to the respective panels on each side of the sewn peripheral first seam. To lessen the degree of pressure loss in the bag, the pressure barrier would extend along the entire length of the structural seam, however this is not a requirement. The pressure barrier preferably extends along all or a defined portion of the structural or first seam. As the air bag is inflated, the panels are pulled apart at the structural seam; the pressure barrier is pushed into the structural or first seam and isolates the seam from the pressurized inflation gas in the air bag, thereby reducing the migration of the inflation gas through the sewn seam and its related needle/thread holes (see FIG. 10). In one preferred embodiment the pressure barrier means is not subject to the peel load as is the first seam, while in another embodiment the edges of the pressure barrier are exposed to such a load.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.